An organic EL device is a self light emitting device and therefore does not require a light source. It has a high luminance and enables a reduction of thickness and reduction of weight. Further, it has a much faster response speed compared with liquid crystal and is superior in displaying moving pictures, so is promising as a display to take the place of liquid crystal devices.
Usually, an organic EL device, as shown in FIG. 1, is structured by a glass substrate 11 on which a first electrode 12 and second electrode 15 sandwich a functional layer 16 comprised of an organic material (electronic transport layer 13 and hole transport layer 14). One device forms one pixel of a display panel. In such an organic EL device, when an electric field is applied between the first electrode 12 and second electrode 15 and electrons are injected into the functional layer from the second electrode 15 and holes are injected from the first electrode 12, the electrons and holes recombine to generate photons 17. That is, electrical energy is converted to light energy.
Organic EL devices may be roughly divided into polymeric types and small molecule types in accordance with the types of the organic materials used for the functional layers. In small molecule type organic EL devices, as functional layers, laminates of organic thin films provided with one of the functions of charge injection, charge transport, and light emission or provided with several of these functions are used.
A conventional bottom emission type organic EL flat panel display is generally produced by the following steps. First, a plurality of transparent electrodes (first electrodes) are formed in patterns corresponding to the pixels at predetermined positions on the glass substrate. For forming the transparent electrodes, a film is formed over the entire surface of the glass substrate by the usual sputtering method, then is patterned by photolithography. Next, functional layers are formed in corresponding patterns on the transparent electrode patterns. Next, back electrodes (second electrodes) are formed on the functional layers. For forming the patterns of the functional layers and the back electrodes, an extremely high positional precision is required. Up until now, ink jet print technology and vacuum evaporation technology using masks have mainly been used for forming the patterns.
On the other hand, in recent years, it has been proposed to use the laser transfer method to pattern the functional layers and the back electrodes and produce organic EL devices. This laser transfer method is a type of dry lithography and is a method suitable for transfer of various thin films (in particular organic films). It has been used for forming color filters of liquid crystals etc. or for providing black matrixes.
A general transfer process using the laser transfer method is shown in FIG. 2. The laser transfer method comprises using a special transfer sheet usually called a “donor sheet”. A typical donor sheet 20 is comprised of a base 21, a photothermal conversion layer 22, an intermediate layer 23, and a transfer layer 24 stacked in that order (FIG. 2(A)). Normally, this donor sheet 20 is placed on the glass substrate or other substrate 25, the transfer layer 24 and substrate 25 are bonded, then laser light 26 is irradiated at predetermined regions of the photothermal conversion layer 22 as shown by the arrows (FIG. 2(B)). In this case, the photothermal conversion layer 22 converts the light energy to heat energy in the irradiated regions. This heat energy is supplied to the transfer layer 24 through the intermediate layer 23 preventing the photothermal conversion layer 22 to invade the transfer layer 24. In this case, the transfer layer 24 is not supplied with heat energy across its entirety. The supply of the heat energy is limited to the parts near the irradiated regions. As a result, the transfer layer 24 is partially heated (FIG. 2(C)). Further, the heated parts stick to the substrate 25. When the donor sheet is then peeled off from the substrate 25, the image components 27 with certain patterns corresponding to the patterns of irradiation of the laser light 26 separate from the intermediate layer 23 and are transferred to the substrate (FIG. 2(D)).